Miniature current-limiting fuses



March 1, 1966 F. J. KozAcKA MINIATURE CURRENT-LIMITING FUSES Filed Dec. l2, 1961 United States Patent 3,238,336 MINIATURE CURRENT-LIMITING BUSES Frederick J. Kozacka, South Hampton, N.H., assigner to The Chase-Shawmut Company, Newburyport, Mass. Filed Dec. 12, 1961, Ser. No. 158,660 Claims. (Cl. 200-131) This invention has reference to miniature currentlimiting fuses, often briefly referred-to as C-L fuses, or CLFs.

It is one object of this invention to provide miniaturized current-limiting fuses, or OLFs, which lend themselves to electronic applications as, for instance, to integration into printed circuits, and which fuses include a pulverulent arc-quenching tller, preferably quartz sand, tending to establish relatively high arc-voltages on blowing of the fuses.

Another object of the invention is to provide ultra compact current-limiting fuses which can be manufactured at relatively small cost and which lend themselves to production by `standard fuse manufacturing methods.

Still another object of the invention is to provide miniature CLF structures including extremely thin fusible silver wires which structures are designed in such a fashion that the thin wire is not likely to be damaged during manufacturing of the structure and when the same is subjected to rough 4handling while in transit.

Further objects and advantages of the invention will become apparent as this description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to, and forming part of, this specification.

For a better understanding of the invention reference may be had to the accompanying drawing wherein:

FIG. l shows-substantially enlarged-a fuse embodying the present invention taken along 1 1 of FIG. 2;

FIG. 2 is a front elevation of a fuse embodying this invention;

FIG. 3 is a top l and 2; and

FIG. 4 shows in longitudinal cross-section a seminished fuse embodying this invention and illustrates a step in manufacturing fuses embodying this invention.

Referring now to the drawings, and more particularly to FIGS. 1 3 thereof, numeral 1 has been applied to indicate generally a tubular casing of insulating material, preferably a synthetic-resin-glass-cloth laminate. Casing 1 includes an axially inner portion 1a having a relatively small outer diameter and casing 1 further includes axially outer end portions 1b having a relatively large outer diameter. Casing 1 m-ay be made of a length of tubing of melamine-glass-cloth laminate of uniform outer diameter by appropriately machining the axially inner portionfof that length of tubing. Metal caps generally indicated by reference character 2 close the ends of casing 1. Each of these terminal caps 2 is mounted on one of the axially outer end portions 1b of casing 1 and each cap 2 has an axially inner edge 2a crimped into engagement with-or at least close to the outer surface of-the axially inner casing portion 1a. Thus caps 2 are firmly secured to casing 1. Each cap 2 defines a center recess 2b which is substantially in the shape of a cone having its narrow or pointed end within the cylindrical space defined by casing 1. Each of caps 2 further defines a center perforation 2c which is situated within recess 2b and substantially at the point where conical recess 2b converges to form a point of minimal cross-section. A relatively thin fusible wire 3, preferably of silver, is arranged within casing 1 and extends in the direction of the longitudinal axis thereof. The two ends of fusible wire 3 project through `the perforations plan view of the structure of FIGS.

2c in caps 2 to the outer conical end surfaces of caps 2. A pair of relatively thick wires 4 form the terminal leads of the fuse structure. Wires 4 are arranged along the axis of casing 1 and each Wire 4 has one end arranged Within one of the receding cones 2b formed by caps 2. Receding cones 2b form solder-receiving cups for conductively connecting the axially inner ends of terminal wire leads 4 to the axially outer ends of fusible silver Wire 3. Reference numerals 5 have been applied to indicate solidified pools of soft solder formed within receding cones 2b serially connecting Wires 4 to the ends of wire 3.

The solder-receiving center recesses 2b must not necessarily be conical in shape, though the conical shape is desirable from the point of view of simplifying the manufacturing process as well as from the point of view of achieving neatly appearing solder joints 5. Numeral 6 has been applied to indicate a pulverulent arc-quenching filler inside of casing 1 in which fusible element 3 is submersed. Filler 6 is preferably quartz sand which yields relatively high arc-voltages and has concomitantly a relatively 4high current-limiting action.

The grain size of the quartz particles inside of casing 1 is larger than the size of perforations 2c in caps 2. Consequently, filler 6 cannot escape through perforations 2c even if solder means 5 have not as yet been established in recesses 2b.

FIG. 4 shows the structure of FIGS. 1-3 while in the process of assembly. Casing 1 has been filled with quartz sand and caps 2 have been mounted on casing 1 and appropriately crimped so as to be lirmly held in position. The next step consists in inserting the thin fusible wire 3. The latter may be threaded by means of a sewing needle through perforations 2c, and when wire 3 is so inserted into casing 1 it is instantly clamped in position by the action of filler 6 and thus not likely to be damaged. The risk of damaging thin silver wire 3 would be considerable if the latter were placed in position inside of casing 1 before filling the latter with quartz sand. The structure of FIG. 4 is ready for receiving the terminal wires 4 and the solder pools 5.

It is apparent from FIGS. l-3 that a CLF embodying the present invention lends itself well to application in printed circuits and to like applications calling for a minimum of bulk combined with a high current-limiting action and a relatively high interrupting capacity.

It will be apparent from the foregoing to those skilled in the art that various changes and modifications may be made without departing from the spirit of the invention as set forth in the appended claims.

I claim as my invention:

1. A miniature current-limiting fuse comprising:

a tubular casing of insulating material;

a pulverulent arc-quenching filler inside the casing;

a pair of terminal caps closing the ends of said casing, each of said pair of caps defining a center recess and further defining a center perforation inside of said recess;

a relatively thin wire extending substantially along the axis of said casing and having ends each projecting through said perforation in one of said pair of caps;

a pair of relatively thick terminal Wires each having an end arranged coaxially with respect to said center recess in one of said pair of caps and projecting into said center recess; and

solder means on the outer surface of each of said pair of caps inside said recess thereof for maintaining said terminal wires in position and conductively connecting said terminal wires and said relatively thin wire.

2. A miniature current-limiting fuse comprising:

a tubular casing of insulating material;

, 0J pulverulent arc-quenching filler inside said casing;

a pair of terminal caps closing the ends of said casing,

solidified pools of solder on said axially inwardly receding surface on each of' said pair of caps for maintaining said pair of terminal wires in position and for conductively connecting said pair of terminal wires t o said fusible wire.

A miniature current-limiting fuse comprising:

a tubularv casing of insulating material;

granular quartz filler inside said casing, said iiller having a predetermined grain size;

a pair of terminal caps closing the ends of said casing,-

each of said pair of caps having a center recess and each4 of said pair of caps dening a perforation situated inside of said recess and being smaller in size than said predetermined grain size to preclude escape of said filler through said recess in each of said pair of caps;

relatively thin silver wireA extending` substantially along the axis of said casingv and having ends each projecting through said perforation in one of said pair of caps tot-he outer surface of one of said pair of caps;

pair of relatively thick terminal wires each havingy an end arranged within said recess vof one ofsaid pair` of cap-s; and

pair of solidied pools of soft solder in said recess of one of said pair of caps. for maintainingr said pair of terminal Wires in position and `for serially connecting said silver wire and said pair of terminal wires. l

A,min iat,u re current-limiting fuse comprising: tubular casing of a synthetic-resinglass-cloth laminate, said casing including an axially inner portion having a relatively small outer diameter and axially outer endportions having a relatively large outer diameter;

granular quartz filler inside said casing;y

pair of terminal caps closingA the endsof saidcasing, each of said pair of caps being mounted on one of said' axially outer end portions of said casing and each ofvsaid` pair ofr caps` having an axially inner edge crimped into engagement with said axial- 'ly inner casing portion, each of said pairV of caps d e ning a center recess and further defining a center perforation inside said recess;

relatively thin wire arranged inside of said casing and having ends each projecting through said perforation in one of said pair of caps to the outer surface of one of said pair of caps;

pair of relatively thick wires each having an end arranged within said recess in one of said pair of caps; and

soft solder means within said recess in eachof said pair of caps conductively connecting said ends` of saidrelatively thin wire to said pair of relatively thick wires and further maintaining said pair of relatively thick wires in position.

. A miniature current-limiting fuse comprising:

tubular casing of a synthetic-resin-glassfcloth laminate, said casing including an axially inner portion having a relatively small outer diameter and axiallyr outer end portions having a relatively large outer diameter;

a granular quartz filler inside of said casing; a pair of terminal caps closing the en ds of said casing,

casing and having ends each projecting through saidk perforation in one of said pair of caps to the outer surface of one l0f said pair of caps;

a pair of relatively thick terminal wire leads each having one end arranged within said recedingv cone of one of said pair of caps;- and pool of solidified soft solder in said receding cone in each of said pair of caps conductively connecting said'ends of said silver wire to said terminal'wire leads and further maintaining said terminal wire leads in position.

References Citedl by the Examiner UNITED STATES PATENTS 1,058,143 4/191'3 Bitter etal. 20G-120 2,296,627 9/1942 Brown 200-131 2,326,031 8/ 1943 Hodnette et al 20G-120 2,713,098 7/1955 Swain 20G-120 2,854,551 9 /1958 Lange 200-131 BERNARD A. GILHEANY, Primary Examiner. {"l" D R, M. SKOLN'IK, Assistant Examiner; 

1. A MINIATURE CURRENT-LIMITING FUSE COMPRISING: A TUBULAR CASING OF INSULATING MATERIAL; A PULVERULENT ARC-QUENCHING FILLER INSIDE THE CASING; A PAIR OF TERMINAL CAPS CLOSING THE ENDS OF SAID CASING, EACH OF SAID PAIR OF CAPS DEFINING A CENTER RECESS AND FURTHER DEFINING A CENTER PERFORATION INSIDE OF SAID RECESS; A RELATIVELY THIN WIRE EXTENDING SUBSTANTIALLY ALONG THE AXIS OF SAID CASING AND HAVING ENDS EACH PROJECTING THROUGH SAID PERFORATION IN ONE OF SAID PAIR OF CAPS; A PAIR OF RELATIVELY THICK TERMINAL WIRES EACH HAVING AN END ARRANGED COAXIALLY WITH RESPECT TO SAID CENTER RECESS IN ONE OF SAID PAIR OF CAPS AND PROJECTING INTO SAID CENTER RECESS; AND SOLDER MEANS ON THE OUTER SURFACE OF EACH OF SAID PAIR OF CAPS INSIDE SAID RECESS THEREOF FOR MAINTAINING SAID TERMINAL SAID RECESS THEREOF FOR MAINTAINCONNECTING SAID TERMINAL WIRES AND SAID RELATIVELY THIN WIRE. 